How can I get Gmail to retain a different default reply-to setting when I change it?

The reply-to field is set when an account is created or updated, and the default setting is what we call the formal alias (first.last@humboldt.edu) to ensure that we have consistency in our email addresses for staff and faculty and to protect user names from getting out into the public domain. Unfortunately, there's no way to override this; any change you make cannot be stored as a new default for this field.